The conventional recording medium, such as an optical disc, is mostly formed by a sole recording layer. Recently, a recording medium having plural recording layers, stacked together, within the disc, has made its debut. In reproducing the optical disc, having plural recording layers, such a method is used that consists in reading out data from one recording layer to another (see for example the Japanese Laid-pen Patent Publication No. 2003-59091).
However, the optical disc, having multiple recording layers, is aimed to improve the recording capacity, and simply data is recorded in each recording layer. Thus, in reproducing the optical disc, data is reproduced from one recording layer to another.